Control apparatus



March 21, 1950 c, sMlTH 2,501,478

CONTROL APPARATUS Filed April 10, 1943 Hume/rim CLYDE E. SMITH 512. ITlME- VOLTAGE Patented Mar. 21, 1950 um'nao STATES PATENT lOFFlCECONTROL APPARATUS Clyde E. Smith, Port Homer, Ohio, assignmto TheTaylor-Winfield Corporation, Ohio, a corporation of Ohio ApplicationApril 10, 1943, Serial No. 482,629

4 Claims. (Cl. 175-32.)

This invention relates to the control of energizing circuits forelectromagnetically actuated devices and more particularly to thesynchronization and time delay of such 'energization with respect to theoccurrence of a reference condition. The principles of the invention areparticularly applicable to electric welding systems or the like, inwhich a heavy current impulse of short or controlled duration issupplied to the load and in which it is desired to eil'ect a sequentialcontrol upon the initiation of or during the flow of welding current.Thus, certain welding methods and apparatus utilize diflerent weldingpressures during the welding cycle and ordinarily the change in pressureis eilected during the flow of welding current. If the particular workat hand or the nature of the predetermined welding cycle is such thatpressure change is to occur near the start of the fiow of weldingcurrent it is obvious that the nature of the control apparatus employedmust be capable, if the control is to be effective, of efiecting thepressure change at an accurately timed interval after the initiation ofthe fiow of welding current as measured in milliseconds of time. .Inco-pending application Serial No. 482,630, filed April 10, 1943, by M.M. A. Seeloff and C. E. Smith, now U. S. Patent No. 2,363,753, there isdisclosed and claimed control arrangements whereby the general objectsare accomplished primarily by energizing an electromagnetically actuateddevice by the discharge oi a capacitor. The object of the presentinvention is to provide a simplified control system for a circuit forenergizing an electromagnetically actuated device wherein theenergization may be accomplished with pulsating half-wave or alternatingcurrent.

According to the present invention the control of the time of theefiecting of the sequential condition is highly accurate withinmilliseconds of time particularly if the condition is to follow closely,i. e., within the time interval represented by the major part of apulsation or half-wave of the energizing current, the appearance of thereference condition which, in welding apparatus,

may be the initiation of the flow of welding current. If the interval ofdelay is to be greater than the time represented by said pulsation orhalf-wave the timing may be efiected in increments of one cycle each andwhile this mode of operation limits the fineness of adjustment over therange of operation this characteristic is usually not objectionablesince the factors making a long delayed interval desirable do notrespond to Warren.

other object of the invention therefore is the provision of a simplifiedand reliable circuit timing the energization of an electromagneticallyactuated device from a pulsating or alternating current source in whicha wide range of adjustment may be eifected but in which, nevertheless,precision in timing may be efiected as required in the case of theactuation of the device following very closely the appearance of thereference condition. In welding thin stock, for'example, and utilizingeither the dischar'e of a capacitor or but a portion of the cycle ofalternating current to effect the weld, if it is desired to eifect achange in the welding pressure exerted during the flow of weldingcurrent the energization of the means efiecting such change must beaccomplished in milliseconds from the initiation of the flow of weldingcurrent. The present in-. vention provides the practical apparatusfor'accomplishing this desired mode of operation.

A further and more specific object of the invention is the provision ofan improved apparatus for controlling the operation of electricresistance welding systems having means to vary the pressure exerted bythe electrodes during the welding cycle.

The above and other specific objects and advantages of the inventionwill become apparent upon consideration of the following detailedspecification and the accompanying drawing wherein certain specificembodiments of apossible application of the principles of the inventionare specifically disclosed.

In the drawing:

Figure 1 is a schematic diagram of a dual pressure electric resistancewelding system utilizing the principles of the invention;

Figure 2 is a curve depicting an electrical characteristic of thecontrol system of Figure 1; and

Figure 3 is a fragmentary schematic diagram of a1 modification of thecontrol circuit of Figure In the drawing the invention is shown, by wayof illustration, as being applied to an electric welding system of thecapacitor discharge type and to this end a principal or power capacitorII is provided and is arranged to be charged from a commercial line Llthrough a charging transformer II and a rectifier ii. In certain systemsof this nature a switch I! is positioned intermediate the rectifier andcapacitor to interrupt the charging circuit during discharge of thecapacitor through the welding load. Normally a weld-' ing transformer I4is employed and suitable precision oi control in this longer range. An-55 means as for example, a contactor. not shownoranelectrmicdischargedevice ilisprovidedtocontrolthedischargeofthecapacitorthrough the primary of the weldingtransformer. TheeecondaryoftheweldingtransformerisconneeteddirectlytotheweldingelectrodesIt and II, one of which is movably supported whereby welding pressuremay be applied therethrough.

The invention is specifically illustrated as being employed for thepurpose of increasing the welding pressure applied by the electrodes apredetermined interval after the initiation of the flow of weldingcurrent. To eilect such operation a presure applying and changing deviceit is positioned intermediate the movable electrode I! and the primaryelectrode moving and pressure ap-.

P11 8 means which may conveniently be a fluid pressure operated cylinderit having a fixed or a readily variable length of stroke. The device IIis disclosed in detail in the above mentioned co-pending application andas stated therein is equipped with a valve II which upon actuationexhausts the fluid pressure in the lower bellows to correspondinglyincrease the pressure exerted by the electrodes. Valve II is arranged tobe opened by a solenoid II the energizing circuit of which will now bedescribed.

Branching from line Ll is a control energy source line L2 and derivingenergy from this latter line is a transformer 22 the secondary of whichis adapted to be connected to the solenoid 1| through the contactor 23of a relay 24 and through the electronic discharge device It. Theresistance and inductance of the solenoid Il may have such absolute andrelated values that the armature of the solenoid may be moved from fullyretracted position to fully actuated position during but a portion ofthe time of current flow in one half cycle of the alternating currentsource in order that the valve will he opened and held open for a lengthof time sufficient to exhaust the small volume of the lower bellowsduring the half cycle interval.

The discharge device 2! is preferably of the gas-filled grid-controlledtype which is normally biased beyond cut-off by a direct currentpotential source 26, .the positive terminal of which is connected to thecathode of device 25 by means of conductor 21 while the negativeterminal is connected to the grid through conductor 28, conductor 2!,the secondary of an impulsing transformer II and the grid resistor Ii.interposed between conductors II and It is a timing capacitor 32 thefunction and operation of which will be explained below. Providing adirect current path around this capacitor is a resistance 33 and apotentiometer 34 in series. Another possible bypass is the resistanceII, the normally closed contactor 3' of the relay 24 and the conductor11. The primary of transformer 80 is connected to a line L! through thevariable resistance 38 the function of which is to phase the impulsefurnished by the secondary of transformer ll at a a ng angle of but afew degrees as will be understood. 1

Timing capacitor 32 is normally maintained in completely dischargedcondition by the parallel circuit consisting of resistor 35, normallyclosed contactor 3t. and conductor 31 and is arranged to be charged at apredetermined rate commencing with the appearance of a referencecondition which in the present case may be the initiation of the flow ofwelding current through the primary of the welding transformer. T sensesuch initiation a transformer ll of the current type is employed, theprimary of which is inserted directly in the current path between thecapacitor II and the transformer ll. A resistance It is connected acrossthe secondary of the transformer it to develop a substantial voltagefrom the current induced in the secondary. In the system illustrated awelding cycle is initiated by admitting fluid pressure to the cylinderII and as the housing of the device ll moves downwardly to move thecommon wall of the two bellows of the device ll into free or floatingposition a switch 4| on the device it closes. Closure of switch llenergires the operating coil 42 of the relay 24 from line Ll throughconductors It, 44 and It. The discharge device II is grid controlled andis normally biased beyond cut-oi! by direct current potential source Itinterposed between the cathode and grid. Included in series in this gridbiasing circuit is the secondary of an impulsing transformer 41 theprimary of which is connected to the secondary of a transformer itthrough the normally open contactor of the relay 24 and the variableresistor II. The primary of transformer It is connected to the line L2and it will be apparent that the voltage applied to the transformer 41will be generally in phase with the anode-cathode voltage of the tube2|. Transformer 4! is so phased that the voltage impulse furnished by itin opposition to the source 46 tends generally to initiate conduction intube It simultaneously with initiation of conduction in tube 25.However, by adjustment of the resistor In the voltage impulse elected bytransformer 41 may be made to occur at the natural power angle of thesolenoid 2i. Thus precise synchronization of the actuation of thecontrol element (valve 20) with respect to the appearance of thereference condition (initiation of conduction in valve II) may beeilected.

Capacitor 32 provides a timing means for delaying the energization ofthe solenoid II a predetermined number of cycles after the initiation ofconduction in valve it if such delay is desired. For reasons to behereinafter pointed out if energfzation of solenoid ii is to be delayedbeyond the particular half cycle utilized to initiate conduction invalve II the timing or adjustment will normally be in one cycle steps.It will be observed that the capacitor 32 as well as being in the gridbiasing circuit for the tube it is also in a series circuit includingpotentiometer 34, an electronic discharge device I, preferably of thegas-filled grid-controlled type, normally open contactor of the relay 2,and capacitor 83. The latter may conveniently be maintained in chargedcondition by a full wave rectifier l4 deriving energy from the line L2through transformer I. Shunting potentiometer 34 and capacitor 82 is aresistor 88 and it will be apparent that upon the closing of contactori2 and conduction in tube ll capacitor I! will be charged to the voltagedeveloped v across resistor 33 at a rate determined by the setting ofthe potentiometer It. As explained above. relay 2 is energized andcontactor I is therefore closed during the welding cycle. Device ii isnormally biased to cut-oil by a direct current potential source Itconnected between the cathode of the device'and one terminal of therea'stance ll associated with the secondar of the transformer It, theother terminal being connected to the grid through the usual gridresistor as shown. Thus upon initiation of the discharge of thecapacitor Ill tube II will be rendered conductive, it being understoodthat the transformer It is so phased that the voltage impulse developedacross appreciable interval of time.

theresist'ancellisinopposltlontothepotential ofthesourcell.

Theeifectoftheriselnpotentialacrossthe capacitor 32 which is in serieswith the grid biasingcircuitforthetube2lisillustratedinFlgure2. Thesmooth dotted curve En represents the charge across the capacitor 32while the lagged solid line E represents the applied grid potential, thesharp proiections from the smooth curve being caused by the impulsesfurnished by the transformer 3l.- The line Ecg represents the criticalgrid biasing potential of the tube 25. It will be apparent thatconduction in. tube 25 will be initiated only during positive pulsesfrom transformer ll which pulses are one cycle apart. However, due tothe adjustment of the resistor 3! as explained above, these pulsesalways occur at the beginning of each positive half cycle so thatsubstantially all the energy contained in the half cycle is madeavailable for the actuation of the parts moved by the solenoid 2| andfor the holding of the parts in actuated positions an If it is desiredto pass alternating current into the solenoid the arrangement of Figure3 may be employed.

In the modification of Figure 3 the single discharge device 25 isreplaced by a pair of similar devices 25! and 252 connected in inverseparallel, the tube 25l being controlled in the same manner as the tube2i in Figure 1. A follow up, transformer 6| is connected across thesolenoid 2| to furnish a grid potential to tube 282 in opposition to thenormal negative biasing potential furnished by a source I to causeconduction in tube 252 following conduction in tube 25]. In themodification of Figure 3 as in the system of Figure 1 the energizingcircuit for the solenoid'is established at the start of a positive halfcycle.

In the system of Figure 1 if the inertia constants of the movable partsof the valve 2| and solenoid 2| are such that the valve will not moveappreciably in a closing direction during the intervening negative halfcycles of the energysource the quantity of energy contained in thatportion of each or any positive half cycle furnished the solenoid needonly be suillcient to eflect full opening of the valve since the tube 2!will continue to conduct in each succeeding positive half cycle due tothe maintenance of voltage on capacitor 82. Upon termination of thewelding cycle and the retraction of the piston in cylinder it the switchII will be opened and the relay 2 de-energized. At this time contactorl3 reestablishes the charging of capacitor ll, contactor 4! enables thebias I to retake control of tube ll, contactor 23 interrupts thesolenoid energizing circuit, contactor S2 breaks the cathode-anodecircuit of tube 5| allowing grid bias 5! to regain control, andcontactor 36 discharges capacitor 22. The parts are thus restored totheir initial conditions preparatory to the carrying out of the nextsucceeding welding cycle.

If it is desired to effect actuation of valve 20 within a very shorttime interval of the initiation of flow of welding current. i. e. withina half cycle of the alternating current source, the potential of source26 is reduced to enable the first positive pulse from transformer 30 toinitiate conduction in tube 25. At a later time-as the current builds upin the solenoid-and as determined by the adiusted value of theresistance il conduction in tube I5 is initiated. This intervalmayequalthecurrentlaginthesolenoidinwhich case the valve will be fullyopened substantially a half y le later if the inertia constants are suchthat a full halfwave is required to effect completion of valve actuationas explained above. The interval may be greater if a very short timingis desired so that conditioning of tube 25 may precede conditioning oftube I I sufilciently to take up a predetermined portion of the powerfactor and mechanical lag thus providing and determining the normallyrequired delay. In this manner the application of the higher pressure orthe eiiecting of other conditions may be accomplished with extreme timedaccuracy.

While the invention has been illustrated in connection with a capacitordischarge welding system employing a series tube to discharge thecapacitor through the welding load it should be understood that certainparts of the invention are equally applicable in systems utilizingmechanical contactors to control the fiow of welding current. Precisesynchronization and consequently accurate short timing cannot then beachieved although the other advantages of the system are retained. Alsothe invention is applicable in welding systems utilizing half wave oralternating welding current as distinguished from direct current derivedfrom the discharge of a capacitor, for example, although in this caseproper operation would require conduction in the discharge device I5 tobe synchronized with the power angle of the welding transformer. Thus,instead of conduction in tube It being controlled in predetermined timerelation to conduction in tube 2! to provide for the timing of solenoidactuation within narrow limits, conduction in tube l5 would besynchronized with respect to the voltage wave of the source and, bearingin mind that the tube 25 should normally be rendered conductive during apredetermined portion of a voltage wave of the source to effect uniformclosing of the solenoid, the adjustment of the timing period will onlybe in one cycle steps. However, in this case, as in the case of thecapacitor discharge system, the timing will be absolutely uniform ineach succeeding welding operation and this characteristic of consistencyis highly desirable.

In connection with the last statement it should be understood that oneof the interrelated functions of the tubes l5 and 25 and one of thefeatures of the invention therefore is that theinitiation of flow ofwelding current (i. e. the firing of tube I5) bears a consistent timerelation to the positive A. C. voltage appearing across tube 25. Insystems wherein welding current flow may be initiated non-synchronouslywith the reference voltage wave the advancing or delaying of the firingof the tube I5 with respect to the reference voltage wave may beutilized to effect adjustment of timing periods in less than one orone-half cycle increments. As required, a capacitor may be shuntedacross resistor 5|! to allow an advancement of the phase position of theimpulse derived from transformer 41. Other specific applications of theinvention are also readily discernible.

The above specifically described embodiments of the invention should beconsidered as illustrative and exemplary only since various changes maybe made therein without departing from the I claim:

1. Apparatus for eflecting movement of an eiectromagnetically operatedmember a timed interval after the appearance of a reference conditioncomprising a source or periodic electrical energy, a circuitinterconnecting said source and the electromagnetic means for operatingsaid member including a circuit controlling device, a timing capacitor,means to vary the charge on said capacitor at a predetermined rate uponthe appearance of said condition, and means operable upon the charge onsaid capacitor reaching a predetermined change in value to initiateconduction in said circuit during a predetermin part of a voltage waveof said source.

2. Apparatus for eflecting movement of an eiectromagnetically operatedmember a timed interval after the appearance of a reference conditioncomprising a source of periodic electrical energy, a circuitinterconnecting said source and the electromagnetic means for operatingsaid member including an electron device having a control grid, abiasing circuit for said grid including means to vary the potentialtherein according to time, means for periodically varying the potentialin said biasing circuit synchronously with said source whereby saiddevice will be rendered conductive during a predetermined part of avoltage wave of said source, and means to render said first namedvarying means operative upon appearance of said condition.

3. Apparatus of the character described comprising in combination meansto establish a condition, a device having electromagnetic operatingmeans, means to energize said last named means from a periodic currentsource, and means utilizing said source to synchronise establishment ofsaid condition withenergintion of said electromagnetic means includingmeans to compensate for the power factor of said electromagnetic means.

4. Apparatus of the character described comprising in combination asource of periodic electrical energy, means establishing a conditionsynchronously with a wave of said source, a device havingelectromagnetic operating means, means to energize said last named meansfrom said source including means to initiate said energizetionsynchronously with said wave, and means to delay the establishment ofsaid condition relative to said energization an interval correspondingto at least the current lag in said eltic means.

CLYDE 1!. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,008,413 Dawson July 16, 19352,077,600 Watson Apr. 20, 1937 2,105,699 Wright Jan. 18, 1933 2,113,664Bimmie Apr. 12, 1938 2,124,795 Roby July 26, 1938 2,134,538 StoddardOct. 25, 1938 2,146,863 Stansbury Feb. 14, 1939 2,227,285 Stansbury Dec.31. 1940 2283,64! Palmer May 19, 1942 2,315,916 Whiteley et a]. Apr. 6,1943

